text: Essentially, the theory states that soft acids prefer to form bonds with soft bases, whereas hard acids prefer to form bonds with hard bases, all other factors being equal. It can also be said that hard acids bind strongly to hard bases and soft acids bind strongly to soft bases. The HASB classification in the original work was largely based on equilibrium constants of Lewis acid/base reactions with a reference base for comparison.
  , should probably be added to the table below -->
  Borderline cases are also identified: borderline acids are trimethylborane, sulfur dioxide and ferrous Fe, cobalt Co caesium Cs and lead Pb cations. Borderline bases are: aniline, pyridine, nitrogen N and the azide, chloride, bromide, nitrate and sulfate anions.
  Generally speaking, acids and bases interact and the most stable interactions are hard–hard (ionogenic character) and soft–soft (covalent character).
  An attempt to quantify the softness of a base consists in determining the equilibrium constant for the following equilibrium:
  :BH + CHHg  H + CHHgB
  Where CHHg (methylmercury ion) is a very soft acid and H (proton) is a hard acid, which compete for B (the base to be classified).
  Some examples illustrating the effectiveness of the theory:
  * Bulk metals are soft acids and are poisoned by soft bases such as phosphines and sulfides.
  * Hard solvents such as hydrogen fluoride, water and the protic solvents tend to dissolve strong solute bases such as fluoride and oxide anions. On the other hand, dipolar aprotic solvents such as dimethyl sulfoxide and acetone are soft solvents with a preference for solvating large anions and soft bases.
  * In coordination chemistry soft–soft and hard–hard interactions exist between ligands and metal centers.